(1) Field of the Invention
The present invention relates to a data communication system, and to a data transmitting apparatus and data receiving apparatus in the system, where simulated bidirectional communication processing is performed between a data transmitting apparatus and a data receiving apparatus using one-way communication, such as a television (TV) broadcast.
(2) Description of the Prior Art
It is now possible to connect personal computers in the home to networks using a standard telephone line and so receive a great variety of information provided by servers around the world. The most representative example of such a network is the World Wide Web (WWW) on the Internet. WWW servers transmit a combination of image information and control information, which has the image information displayed within text information, to personal computers as the data for displaying a one-page image on the personal computer""s screen. When such pages are made up of text information alone, only control information for displaying this text information is transmitted. This control information is written using HTML (HyperText Markup Language), with browser software executed by the personal computer decoding and executing the HTML code to display each page on the WWW which is downloaded by the user. Here, information indicating a link to another page can be attached to character strings and images in a page, so that when the user makes a selection operation for such a character string or image using a mouse, for example, the browser will access the WWW server that provides the indicated page and will obtain the information for displaying this new page. On obtaining this information, the browser will decode and execute its content to display the new page.
Japanese Laid-Open Patent Application 7-322226 (1995) discloses a method for multiplexing control information that can generate the kind of interactive display described above into a TV broadcast which is transmitted using a TV broadcast ground wave. In this method, the program transmitting apparatus multiplexes data, written in a language which resembles HTML for composing an interactive screen, into a program broadcast before transmitting. On receiving this broadcast, the program receiving apparatus interprets the composition of the interactive screen and combines basic display elements which have been stored inside its structure in accordance with the indicated composition to compose the interactive screen.
The above method has a major drawback in that the control information is written in a language for indicating a variety of control operations which are performed for display, so that the receiving apparatus needs to interpret and execute these control operations one by one to perform display. Additionally, most high resolution images provided by WWW servers are compressed using complex techniques, so that when a receiving apparatus attempts to display such image information, it is usually necessary to perform decompression in addition to the processes for display in accordance with the control information. Since such complex processing is required, the load of the receiving apparatus is considerable, which greatly increases the cost of the necessary hardware for the receiving apparatus.
With the above program receiving apparatus, the contents of a broadcast program cannot be changed interactively through a composed interactive screen.
It is therefore the first object of the present invention to provide a transmitting apparatus, a receiving apparatus, a receiving method, a recording medium for recording a receiving program, and a communication system, for performing simulated bidirectional processing between a data transmitting apparatus and a data receiving apparatus without increasing the load of the data receiving apparatus in a one-way communication system, such as a TV broadcast.
A transmitting apparatus which can achieve the above object should comprise: a first storing unit for storing a plurality of frames of image data; a second storing unit for storing control information showing links between the plurality of frames of image data stored in the first storing unit; and a transmitting unit for repeatedly transmitting a predetermined number of frames of image data together with corresponding control information.
The transmitting apparatus having this structure repeatedly transmits image data and corresponding control information. The receiving apparatus can receive the linked image data expressed by the control information without fail, so that users can interactively trace from one frame of image data to another. As a result, users can feel as if having a bidirectional communication using a one-way broadcast wave.
With a conventional bidirectional server, the load greatly varies depending on the amount of request from the receiving apparatus, which have influence on the response time from receiving an operation instruction until switching display images. On the other hand, the load of the transmitting apparatus of the present invention does not vary so that the repetitive transmission cycle can be fixed. Thus, in the receiving apparatus of the present invention, image data can be switched within a predetermined response time, that is, within one cycle of the repetitive transmission.
The transmitting unit of the transmitting apparatus may comprise: a reading unit for repeatedly reading a predetermined number of frames of image data together with corresponding control information from the first and second storing units; a multiplexing unit for multiplexing image the image data and the corresponding control information read by transmitting them in the image area and retrace area, respectively, of a television signal; and an output unit for outputting the multiplexed television signal as an analog broadcast wave. With this structure, an analog broadcast wave can be utilized in realizing the interactive communication.
The image data and control information stored in the first and second storing unit may be digitized, and the transmitting unit may comprise: a reading unit for repeatedly reading a predetermined number of frames of image data together with corresponding control information from the first and second storing units; a multiplexing unit for converting image data and control information into digital data streams, and then multiplexing the digital data streams so as to produce a multiplexed stream; and an output unit for outputting the multiplexed stream as a digital broadcast wave.
With this structure, a digital broadcast wave can be utilized in realizing the interactive communication.
The first and second storing units may store image data and corresponding control information as well as identifiers. The transmitting apparatus may further comprise a third storing unit for storing audio data corresponding to the image data, with the same identifiers being allotted to the corresponding image data and control information. Here, the transmitting unit may transmit the audio data as well as the image data.
With this structure, sets of image data and audio data can be transmitted to achieve a more attractive interactive communication.
The transmitting apparatus may comprise: an obtaining unit for obtaining page information expressing a plurality of pages containing characters and images; a first producing unit for producing one frame of image data containing characters and images in accordance with character information and image information included in the obtained page information; and a second producing unit for producing control information showing links between frames by interpreting the link information included in the obtained page information.
With this structure, page information obtained from outside can be converted into image data and control information suitable for broadcasting.
The obtaining unit of the above transmitting apparatus can obtain page information from the World Wide Web on the Internet.
The transmitting apparatus of this structure converts HTML documents of the WWW server on the Internet into image data and control information for broadcasting. By doing so, interactive broadcast programs which users can enjoy as if doing xe2x80x9cNet surfingxe2x80x9d on the Internet can be provided using a TV broadcast wave.
In order to achieve the above object, the receiving apparatus should comprise: a separating unit for separating a frame of image data and corresponding control information from the broadcast wave produced by multiplexing a plurality of frames of image data and control information showing links between the plurality of frames of image data; a storing unit for storing the separated image data and control information; a reproducing unit for reproducing the stored image data to output an image signal; an operation unit for receiving an operation instruction to switch image data; and control unit for controlling the separating unit so as to separate another frame of image data designated by the control information stored in the storing unit according to the operation instruction.
The receiving apparatus having this structure receives a broadcast wave from the transmitting apparatus, and performs the processing of separating a frame of image data, reproducing it, and then outputs an image signal, according to the operation instruction. This receiving apparatus can receive linked image data expressed by the control information with certainty in the repetitive transmission, so that users can trace the desired linked image data successively. As a result, users can feel as if having a bidirectional communication using a one-way broadcast wave. With a conventional bidirectional server, the load greatly varies depending on the amount of request from the receiving apparatus, which have influence on the response time from receiving an operation instruction until switching display images. On the other hand, the load of the transmitting apparatus of the present invention does not vary so that the repetitive transmission cycle can be fixed. Thus, in the receiving apparatus of the present invention, image data can be switched within a predetermined response time, that is, within one cycle of the repetitive transmission.
In this receiving apparatus, the identifier allotted to a frame of image data is the same as the identifier allotted to corresponding control information, and the control information expresses the identifier allotted to the linked image data. The separating unit of such a receiving apparatus may comprise a first detecting unit for detecting the identifier allotted to the image data, a second detecting unit for detecting the identifier allotted to the control information, and an obtaining unit for obtaining the image data and control information if the first and second detecting units have detected the identifiers. The storing unit of this receiving apparatus stores the image data and control information obtained by the obtaining unit.
To this receiving apparatus, image data and control information are transmitted in the image area and retrace area, respectively, of a television signal as a multiplexed analog broadcast wave. An identifier to be shown as an image at a fixed position in the non-displayed part of the image area is transmitted in the broadcast wave. The first detecting unit recognizes an identifier from the image at the fixed position in the non-displayed part.
The same identifier is allotted to image data and corresponding control information transmitted to this receiving apparatus. The image data and control information have been converted into digital data streams to be multiplexed to transmit a multiplexed stream as a multiplexed digital broadcast wave. The digital data streams are allotted first identifying information to identify image data and second identifying information to identify control information. The multiplexed stream is produced by multiplexing the digital data streams and a map table. The map table shows the correspondence between the first identifying information and image data identifiers as well as the corresponding between the second identifying information and control information identifiers. The storing unit of this receiving apparatus stores a map table separated by the separating unit. The control unit of this receiving apparatus recognizes an identifier allotted to linked image data expressed by control information, converts the identifier into first identifying information and second identifying information referring to the map table, and sets the first identifying information and second identifying information to the separating unit. The separating unit comprises a first detecting unit for detecting the first identifying information from the multiplexed stream, a second detecting unit for detecting the second identifying information from the multiplexed stream, and an obtaining unit for obtaining image data and control information indicated by the first and second identifying information detected by the first and second detecting units.
The control information may express at least one combination of a coordinate showing the image part of the corresponding image data and the identifier allotted to the linked image data. The operation unit of this receiving apparatus receives an operation instruction to designate the image region in the image data. The control unit of this receiving apparatus read the identifier allotted to the linked image data corresponding to the designated image region, and sets the identifier to the separating unit.
The separating unit may further separate audio data, the storing unit stores the separated audio data, and the reproducing unit reproduces the stored audio data to output an audio signal.
With this structure, sets of image data and corresponding audio data are received and reproduced, so that more attractive interactive communication can be realized.
In order to achieve the above object of the present invention, a receiving method should comprise the steps of: separating a frame of image data and corresponding control information from the broadcast wave produced by multiplexing a plurality of frames of image data and control information showing links between the plurality of frames of image data; storing the separated image data and corresponding control information; reproducing the image data stored in a memory to output an image signal; receiving an operation instruction to switch image data; detecting image data indicated by the control information stored in a memory according to the operation instruction; and separating the detected image data and corresponding control information from the broadcast wave.
A communication system which can achieve the above object should comprise the above-mentioned transmitting apparatus and the receiving apparatus.